Die cushion



Oct. 13, 1964 D. H. GARDNER 3,152,564

DIE CUSHION Filed Sept. 11, 1961 W W 36H n 5 4 IN ENTOR.

DONALD HENRY GARDNER BY ATTORNEY United States Patent 3,152,564 DIE CUSHION Donald Henry Gardner, Cranston, RI, assignor to Elastic Die Engineering Company, Warwick, R.I., a corporation of Rhode Island Filed Sept. 11, 1961, Ser. No. 137,290 4 Claims. (Cl. 11346) This invention relates to punch and die sets and more particularly to an improvement in the die cushion.

A punch and die set is an assembly consisting of an upper member called the punch holder and a lower member called the die holder. The under surface of the punch holder and the top surface of the die holder are those on which the punch and die sections of a punch press tool are mounted. In use the die holder is clamped to the bed of a punch press, while the upwardly extending punch holder shank is fastened in the clamping orifice provided in the reciprocating punch press ram. The punch is actuated by the reciprocating motion of the ram. Mating guide posts and bushings of an assembled die set assist in maintaining punch and die set alignment during the operation of the punch press.

The present invention is directed to punch and die sets in which the die holder is provided with a movable pressure ring. In the past there have been many different types of movable pressure rings. For example, United States Patent #l,4-75,437 is directed to a spring resistant pressure ring, which enables the pressure ring resistance to be readily, precisely and extensively varied. In United States Patent #l,556,6l1 the movable pressure ring is provided with fluid pressure resistance in the form of a vacuum. This was declared to be an improvement over other hydraulic fluid pressure resistant pressure rings. In United States Patent #l,606,l4l electro-magnetic means is employed upon the pressure ring so it can grip the work piece and hold it with the desired degree of pressure. And in United States Patent #1,56l,770 a cam connected to the pressure ring is oscillated from a rotating part of the press. This connection is elfected directly or through a resilient buffer associated with the pressure ring. It is evident that problems have always existed in movable pressure ring die holders because so many different types of mechanisms have been employed to solve the problems.

Movable pressure rings are employed in die sets to permit metal blanks to be shaped and drawn and at the same time prevent the margin of a metal blank-from wrinkling or cracking while it is drawn or shaped.

Past movable pressure ring devices limited the drawing operation to between twenty-five and thirty percent of the diameter of the metal or work blank. That is, a three inch diameter work blank struck by a one and one-half inch diameter punch permitted to draw of approximately three-eighths of an inch. If a deeper draw was needed, two additional successive draw operations would be required to produce a three-quarter inch draw.

It is therefore an object of the present invention to provide a die cushion or movable pressure ring with a construction which will provide a minimum of a fifty percent draw in a single punch press operation while eliminating wrinkling or cracking in the blank.

It is another object of the present invention to provide a die cushion which will accurately transfer the minutest detail of design from a punch to a work blank.

It is still another object of the present invention to required to produce a given depth of deep draw and shapes metal blanks with a greater degree of accuracy than was heretofore known.

A further object of the present invention is to provide a die cushion which reduces the number of operations required to produce a given depth of deep draw and which does not change the gage of the blank in the drawing and shaping operation.

Other objects of the present invention will become apparent in part and be pointed out in part in the following specification and claims.

Referring to the drawings in which similar characters of reference indicate corresponding parts in all the fig ures:

FIGURE 1 is a plan view of a punch and die set embodying the present invention.

FIGURE 2 is a side elevational View of FIGURE 1.

FIGURE 3 is a vertical cross sectional view taken along mline 33 of FIGURE 1.

FIGURE 4 is a horizontal cross sectional view taken along line 44 of FIGURE 3.

FIGURE 5 is a view similar to FIGURE 3 showing the die in engagement with the punch.

In proceeding with this invention, reference numeral iii, generally designates the new and improved punch and die set. In the prior art and in prior practice plate 11 would serve as the punch holder and plate 12 the die holder. In the instant application plate ii is the die holder and plate 12 is the punch holder. The instant application reverses the position of the punch and die holders for reasons which will presently appear. A shank 13 may form an integral part of plate 11 or be secured thereto as by welding. A die 2 9 preferably fabricated from steel is provided with a configuration 21 and an outside diameter 23. A plurality of dowel pins 17 and a plurality of screws Iii secured die 20 to the underside 25 of plate ill. A knockout pin 27 having a head 28 is slidably mounted (see FIGURE 3) in die 2%, plate 11 and shank 13 with head 28 located in die 29. Pin 27 is provided with a slot 30. A pin 31 removably secured in shank 13 extends into slot 349 to prevent knockout pin 27 from falling out of its guideway 32 in shank 13, plate 11 and die 20. Plate 11 is provided with a plurality of conventional die bushings, illustrated as two in number, 33, 34. Plate 12 is provided with the die posts 35, 36 conventional to die sets, which slidably engage die bushings 33, 34, respectively.

Lower plate 12 may be recessed, as illustrated in FIG-.

URE 3, to provide a base 37 having a circular side wall 33. A steel collar 49 having an outside diameter 4 1 and an inside diameter 42 is secured to said base 37 with outside diameter 41 abutting side wall 38.

A punch stand 50 is secured to lower plate 12 as by welding or as illustrated by means of screw 51. A punch 52 provided with any desired contour or design, but illustrated as a circular cap is fastened to punch stand 50 by means of a dowel pin 53. A die cushion 55 of polyurethane material having an inside diameter 56 and an outside diameter 57 is provided between punch stand 50 and steel collar 40. There is a clearance between inside diameter 56 of die cushion 55 and outside diameter 58 of punch stand 56. There is clearance between outside diameter 57 of die cushion 55 and inside diameter 42 of collar 40. The last two mentioned clearances are provided for purposes which will presently appear. Punch 52 and punch stand 5d may be fabricated from one piece of material or from two separate pieces of material as illustrated.

A movable pressure ring or pad fabricated from rigid material such as steel is provided with an inside diameter 76 and an outside diameter 77. Movable pressure ring 75 on the inside diameter 76 is provided with a contour which mates with punch 52. Movable pressure ring 75 is slidably mounted upon punch 52 and slidingly engages inside diameter 42 while being supported by end 78 of polyurethane die cushion 55. A work piece may overlie steel movable pressure ring 75.

Polyurethane material inherently possesses the physical characteristic of uniform expansion and uniform contraction when compressed or when force is removed therefrom. Uniform expansion means that force applied to one end of die cushion 55 for example, Will cause outside diameter 57 and inside diameter 56 to expand equally along the entire surface of the inside and outside diameters and not bulge, as a balloon, such as a weak spot in an inner tube. A spring acts as a weak spot in an inner tube when compressed because the end convolutions compress to a maximum capacity before the compression force is transferred to the next adjacent convolution. Natural and conventional rubbers react to compression in a manner similar to a spring. It is the uniform expansion and contraction characteristics which, in part, make the present die cushion possible. Another physical characteristic of polyurethane is that it has an elongation capacity up to six hundred and fifty percent of its length. This is ten times greater than natural or synthetic rubber.

A polyurethane material having the following physical characteristics provides the most satisfactory die cushion. A durometer reading of ninety-five (95) but not less than seventy (70). An elongation potential of approximately six hundred fifty percent (650%) but not less than five hundred percent (500%). A normal elongation of two hundred percent at eighteen hundred pounds per square inch pulling force. A minimum tensile strength of fortythree hundred pounds per square inch. One such polyurethane material is commercially known as Elastacast.

Applicant has utilized these natural characteristics in redesigning a die set which functions in the following manner.

A work piece or sheet metal blank ltl-tl is placed upon movable pressure ring 75. The reciprocating ram of a press (not shown) will cause die carrying plate 11 through bushings 33, 34 to move toward and away from punch carrying plate 12 as bushings 33, 34 slide upon die posts 35, 36. In the initial downward stroke of the reciprocating movement, surface 191 of die 2d will engage sheet metal blank 109 and force said blank against movable pressure ring '75. Continued downward movement of die 20 will cause metal blank 1% to form around punch 52 while movable pressure ring 75 slides between punch 52, punch stand 50 and inside diameter 42.

The critical features of the present invention and applicants contribution to the art is the discovery that a die cushion 55 fabricated from a material which offers a constant and uniform resistance, and not an increased resistance, to the downward movement of the die, produces a punch and die product which retains the gage of the material after formation and with a depth of draw in one operation which heretofore was obtainable only after a series of drawing operations.

It is not only desirable but necessary that the die 29 engage and form the blank Hill with a constant uniform pressure. If the pressure ring 75 olfers more resistance to one side of the die than the other side of the die 20, then the die 20 engages the blank 16% out of vertical alignment causing an elongated stamping. The uniform pressure pad 75 allows the metal of blank lltltl to slide or flow evenly off the pressure ring 75 and around the radius of the die 20 and up and over the punch 52. If the pressure increases or is uneven then the metal blank will snag between the pressure ring 75 and die 21) so that the punch 52 will rupture the material. If the pressure decreases the material will wrinkle between the pressure ring 75 and die 20. The blank ltlt) is thereby ruined.

As illustrated die cushion 55 may be circular in cross section. Die cushion 55 is held in desired position by inside diameter 42 and outside diameter 58. The clearance is provided between outside diameter 58 and inside diameter 56 and between outside diameter 57 and inside diameter 42 in order to allow die cushion to expand when compressed by the action of die 20 upon pressure ring or pad 75.

aving shown and described a preferred embodiment of the present invention by way of example, it should be realized that structural changes could be made and other examples given Without departing from either the spirit or scope of this invention.

What I claim is:

l. A punch and die set comprising a die holding plate provided with a plurality of die bushings and a shank, a punch holding plate provided with a plurality of die posts adapted to slidingly engage said plurality of die bushings, a die, means fastening said die to said die holding plate, a die cushion collar, means securing said die cushion collar to said punch carrying plate, a punch, means securing said punch to said punch carrying plate, a die cushion fabricated from polyurethane material, located within said die cushion collar and surrounding said punch, a movable pressure ring slidably mounted within said die cushion collar and lying upon said die cushion, whereby relative movement of said die holding plate toward said punch holding plate engages said die with said punch, said die engaging said movable pressure ring and thereby depressing said die cushion, said die cushion uniformly resisting engagement of said die with said movable pressure ring.

2. A punch and die set comprising a die holding plate provided with a plurality of die bushings, a punch holding plate provided with a plurality of die posts adapted to slidingly engage said plurality of die bushings, a die, means fastening said die to said die holding plate, a die cushion collar circular in cross section, means securing said die cushion collar to said punch carrying plate, a punch, means securing said punch to said punch carrying plate, a hollow die cushion circular in cross section fabricated from a polyurethane material having the physical characteristics of a durometer reading of approximately ninety-five, an elongation potential of approximately six hundred percent, a normal elongation of approximately two hundred percent at eighteen hundred pounds per square inch and a tensile strength of approximately forty-three hundred pounds per square inch, said hollow die cushion located around said punch and within said die cushion collar, a movable pressure ring slidably mounted within said die cushion collar and lying upon said die cushion, whereby relative movement of said die holding plate toward said punch holding plate forces a blank lying upon said movable pressure ring to be formed to the contour of said punch and die upon the mating of the punch and die, said die cushion uniformly resisting engagement of said punch and die through said pressure ring and blank.

3. A punch and die set comprising a die holding plate provided with a plurality of die bushings and a shank, a punch holding plate provided with a plurality of die posts adapted to matingly engage said plurality of die bushings for sliding engagement, a die provided with a contour, means fastening said die to said die holding plate, a die cushion collar having a hollow axial area circular in cross section, means securing said die cushion collar to said punch carrying plate, a punch stand circular in cross-section, means securing said punch stand to said punch carrying plate, a punch, having a contour mating with the contour of said die, means securing said punch to said punch stand, a hollow die cushion circular in cross section fabricated from a polyurethane material having the physical characteristics of a durometer reading of approximately ninety-five, an elongation potential of approximately six hundred percent, a normal elongation of approximately two hundred percent at eighteen hundred pounds per square inch and a tensile strength of approximately forty-three hundred pounds per square inch, located within said hollow axial area and surrounding said punch stand, a movable pressure ring having a circular outside diameter adapted to slidingly engage said hollow axial area and having an axial contour adapted to slide over said punch, and lying upon said hollow die cushion.

4. A punch and die set comprising a die holding plate provided with a plurality of die bushings and a stand, a punch holding plate provided with a plurality of die posts adapted to slidingly engage said plurality of die bushings, a die, means fastening said die to said die holding plate, a die cushion collar fabricated from rigid material, means securing said die cushion collar to said punch carrying plate, a punch, means securing said punch to said punch carrying plate, a die cushion fabricated from polyurethane material located within said die cushion collar and surrounding said punch, a movable pressure ring slidably mounted Within said die cushion collar and lying upon said die cushion, and an inverted T shaped guideway located in said die, in said die holding plate and in said shank with the cross arm of the T located in said die, a T shape knock out pin provided with a slot, slidably mounted in said guideway, a pin secured in said shank and extending into said slot to limit the sliding movement of said knock out pin, relative movement of said die holding plate toward said punch holding plate engages said die with said punch, said die engaging said movable pressure ring against the constant uniform resistance of said die cushion.

References Cited in the file of this patent UNITED STATES PATENTS 2,132,002 Hight Oct. 4, 1938 2,321,075 Frey et a1 June 8, 1943 2,331,491 Menkin Oct. 12, 1943 2,899,922 Wheeler Aug. 18, 1959 2,998,238 Kenline Aug. 29, 1961 3,022,758 Rheingold et al Feb. 27, 1962 FOREIGN PATENTS 21,862 Norway Nov. 27, 1911 

1. A PUNCH AND DIE SET COMPRISING A DIE HOLDING PLATE PROVIDED WITH A PLURALITY OF DIE BUSHINGS AND A SHANK, A PUNCH HOLDING PLATE PROVIDED WITH A PLURALITY OF DIE POSTS ADAPTED TO SLIDINGLY ENGAGE SAID PLURALITY OF DIE BUSHINGS, A DIE, MEANS FASTENING SAID DIE TO SAID DIE HOLDING PLATE, A DIE CUSHION COLLAR, MEANS SECURING SAID DIE CUSHION COLLAR TO SAID PUNCH CARRYING PLATE, A PUNCH, MEANS SECURING SAID PUNCH TO SAID PUNCH CARRYING PLATE, A DIE CUSHION FABRICATED FROM POLYURETHANE MATERIAL, LOCATED WITHIN SAID DIE CUSHION COLLAR AND SURROUNDING SAID PUNCH, A MOVABLE PRESSURE RING SLIDABLY MOUNTED WITHIN SAID DIE CUSHION COLLAR AND LYING UPON SAID DIE CUSHION, WHEREBY RELATIVE MOVEMENT OF SAID DIE HOLDING PLATE TOWARD SAID PUNCH HOLDING PLATE ENGAGES SAID DIE WITH SAID PUNCH, SAID DIE ENGAGING SAID MOVABLE PRESSURE RING AND THEREBY DEPRESSING SAID DIE CUSHION, SAID DIE CUSHION UNIFORMLY RESISTING ENGAGEMENT OF SAID DIE WITH SAID MOVABLE PRESSURE RING. 